1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus.
2. Description of Related Art
In general, an electrophotographic image forming apparatus (such as a printer, a copy machine, and a fax machine) is configured to irradiate (expose) a charged photoconductor with (to) laser light based on image data to form an electrostatic latent image on the surface of the photoconductor. The electrostatic latent image is then visualized by supplying toner from a developing device to the photoconductor (image carrier) on which the electrostatic latent image is formed, whereby a toner image is formed. Further, the toner image is directly or indirectly transferred to a sheet through an intermediate transfer belt, followed by heating and pressurization for fixing, whereby an image is formed on the sheet.
The above-described image forming apparatus includes a conveyance section for conveying to an image forming section a sheet fed from a sheet feed tray, a manual feed tray or an external paper feeding apparatus. In the sheet conveyance section, a plurality of conveyance roller sections including an intermediate conveyance roller section, a loop roller section, a registration roller section and the like are disposed, for example.
In the sheet conveyance section, a sheet is continuously conveyed by the loop roller section even after the leading edge of the sheet reaches the registration roller section, whereby the sheet is bent between the registration roller section and the loop roller section and a skew of the sheet is thus corrected.
In addition, the sheet conveyance section is provided with a displacement correction section for correcting the lateral position of sheets (horizontal scanning direction). For example, the registration roller section conveys a sheet while translating in the lateral direction (axial direction of the registration roller), thereby correcting the lateral position of the sheet (registration translation). The registration translation operation is performed based on a result of detection (displacement amount and deviation from a standard position) by a displacement detection sensor such as a line sensor disposed on a downstream side of the registration roller section.
When the displacement amount of the sheet is within the range which can be covered by the translation of the registration roller section (for example, ±5 mm), the lateral position of the sheet can be surely corrected by the registration translation. However, when the displacement amount of the sheet falls outside the range of the translation of the registration roller section, the lateral position of the sheet cannot be corrected by the registration translation, resulting in a displacement error. Under such a circumstance, in the case where a displacement error is detected by the displacement detection sensor, an image formation process is stopped by causing a jam.
In addition, there are proposed image forming apparatuses in which an image formation process is stopped when a skew of a sheet is not corrected and when a sheet (arrangement of front and back of sheets) is improperly stored in the sheet feeding section (for example, Japanese Patent Application Laid-Open Nos. 2002-362781 and 2005-136738).
The displacement error may occur in the image forming apparatus when a foreign substance such as paper debris remains in a sheet conveyance path, when the state of sheets stored in the sheet feed tray is poor due to factors such as a sheet in a folded state and an insufficient side regulation in the sheet feed tray (improper setting), and when a displacement of a sheet is reflected to an image formation on the back surface of the sheet (during the sheet conveyance) since the displacement correction section has not appropriately operated during an image formation on the front surface of the sheet (during the sheet conveyance), for example.
However, since conventional image forming apparatuses only stop the image formation process by causing a jam when a displacement error is detected, it is difficult for a user to recognize the cause of the displacement error. Therefore, the cause of the displacement error may not be eliminated when a user performs jam clearance. When the cause of the displacement error is not eliminated, a jam due to a displacement error is again caused. In this manner, the conventional handling methods are not efficient and lead to decrease in productivity.